1. Field of the Invention
The invention relates to a method and a device for cleaning an item to be cleaned, and to a corresponding computer program. The cleaning method ensures in particular a thermal hygiene effect, in particular an improved long-term hygiene effect. The method can also be used to compensate for the so-called “lag of regrowth effect”. Such cleaning methods and cleaning devices may be used for example in the natural sciences, technology, medicine or healthcare technology in order to subject various types of items to be cleaned to cleaning and hygienization, extending as far as disinfection. Application examples are dishwasher technology or the cleaning of healthcare utensils.
2. Description of the Background Art
In many fields of daily life, technology, the natural sciences and medicine and/or the healthcare sector, cleaning devices for a multiplicity of objects to be cleaned are known from the prior art. As examples, which do not however restrict the possible application scope of the present invention, dishwasher machines may be mentioned which are employed in the household sector or for example in the industrial sector as single-chamber or multiple-chamber dishwasher machines. As another example, cleaning devices for medical equipment and/or healthcare equipment may be mentioned, in particular containers which receive large amounts of liquid as waste. For example, cleaning-disinfection equipment may be mentioned here, which can be used for example to clean chamberpots, bedpans, urine bottles, night-time utensils or similar containers and instruments from the medical sector or healthcare sector.
Many cleaning devices are used to clean items to be cleaned, which come directly or indirectly in contact with possibly germ-laden materials. As examples to be mentioned here are objects which enter indirectly or directly in contact with the human body and can therefore act as transmitters of diseases, in particular infections, and for which particular value is therefore to be placed on sufficient hygienization, i.e. sufficient germ reduction, extending as far as disinfection.
Measuring and ensuring a hygiene level and/or germ reduction is the subject of many known methods and standards. In particular, with action of wet heat on the item to be cleaned, a relationship of temperature and time to the germ reduction in multiple-tank dishwasher machines has been studied. For example, DIN 10510 establishes minimum requirements for Germany in respect of temperature, cleaning-agent concentration and time between first contact of the item to be cleaned with the washing liquid until leaving the machine. The basis of this standard is the germ reduction of test bodies, contaminated in a defined way, after the cleaning process by means of so-called contact tests. In this test, E. faecium ATCC 6057 is used as a test germ or organism.
Testing the hygiene reliability of multiple-tank dishwashers at the end user is generally carried out by contact tests and determining the germ count in the wash water of the last washing tank. A disadvantage with this method, however, is the fact that testing of the germ reduction in situ at the customer according to this standard can only be carried out with great outlay. Another disadvantage of this standard is the fact that the same germ reduction could for example also be achieved with a shorter contact time but at higher temperatures in the individual treatment zones. The said standard does not allow for this.
Accordingly, there are standards which determine the hygienization effect of the cleaning equipment by means of cumulative heat equivalents. As explained in more detail below, heat equivalents generally refer to integrals or sums over a time profile of the temperature or a function value of a monotonically increasing function of the temperature, to which the item to be cleaned is exposed. The temperature is conventionally weighted according to an established weighting function or converted directly into weighted values.
In the USA, for example, the relationship of temperature and time to the germ reduction is described by the so-called NSF3 standard method. The basis of this specification is the germ reduction, determined from tests, of tuberculosis bacteria by the effect of temperature over time. The effect of temperature over time is referred to as a heat equivalent. In this method, a table records how many heat equivalents are achieved at which temperature. As a minimum temperature beyond which heat equivalents are counted, a temperature of 62° C. (corresponding to 143° F.) is mentioned according to this standard. For dishwashers, this usually means that at least 3600 heat equivalents must be reached according to this specification in order to fulfil the required germ reduction. An advantage of this method is that the method can be carried out in situ with relatively little outlay, in order to check correct functioning of a dishwasher machine in respect of thermal hygienization.
There are also corresponding standards in Germany and Europe. For example, for cleaning-disinfection equipment, EN ISO 15883-1 describes a method which is used to assess the hygiene effect likewise in the relationship between the germ reduction and the temperature over time. This relationship is also referred to as the A0 value, and is likewise recorded in tabular form or calculated from a mathematical formula. The A0 value is described in more detail in Annex A of this standard, and is defined as the time equivalent in seconds at 80° C. for which a given disinfection effect is exerted; it corresponds in essence to the procedure in the NSF3 standard but while being based on a different test germ.
The A0 concept was developed in the scope of the European standardization work for disinfection methods. It came from the desire to make the efficacy control of thermal disinfection methods more transparent and the approval of disinfected items independent of microbiological control cultures (parametric approval). The A0 concept is based on the assumption that a defined amount of energy, defined by temperature and action time, is necessary for the reproducible inactivation of a particular microbe load. This is in analogy with the F concept for the thermal sterilization of medical items, although in that case much higher amounts of energy are necessary than for disinfection. The A0 concept involves assumptions which were made on the basis of empirical values concerning the thermal killing of microbes. The experimental bases, however, are sketchy and sometimes contradictory. A systematic experimental verification of the assumptions of the A0 concept with different microbe classes has not yet been carried out.
According to the standard EN ISO 15883-1 (cleaning and disinfection equipment—Part 1: General requirements, definitions and tests), thermal disinfection with wet heat in cleaning and disinfection equipment (CDE) is defined and monitored parametrically by means of the A0 value. This represents the applied energy as a product of applied temperature and action time. Biological indicators as time-consuming and variable “measuring sticks” for approval of the item to be disinfected are therefore largely obviated and replaced by registering physical parameters. The starting point is the A value, which represents a time equivalent in seconds at 80° C. for which a given disinfection effect is achieved. The following measurement units are important for the A0 concept:
The microbiological parameter referred to as decimal reduction time or D value, as a measure which characterizes the thermal death behaviour of microorganisms. The D value indicates the time which is necessary to kill 90% of the microorganisms of a population at a given temperature T, i.e. to reduce the population to 10% of the initial number. The D value therefore represents a measure of the heat sensitivity of a particular microorganism type.
The dependency of the D value on the temperature T is recorded by a z value. The z value indicates the temperature increase which is necessary in order to reduce the D value by 9/10, i.e. to achieve the same killing effect in one tenth of the time.
The AQ value is the A value for microorganisms whose z value is 10° C.; for the A0 concept, the assumption is z=100 C. This assumption, together with the basic thesis that the same disinfection effect can be achieved both by higher temperature and shorter action time, and by lower temperature and correspondingly longer action time, gives a well-reproducible and practicable concept for dealing with thermal disinfection methods.
In EN ISO 15883-1, A0 values of 60, 600 and 3000 are proposed for practical purposes, depending on the importance of the freedom from germs; an A0 of 3000 means 50 times the amount of energy compared with an A0 of 60 and achieves a much better disinfection effect. Table 1 presents examples of temperatures and times for the respective A0 values.
TABLE 1Time equivalents for various A0 values.TemperatureA060A0600A0300070° C.10min100min500min75° C.3.2min32min160min80° C.1min10min50min85° C.0.3min3.2min16min90° C.6s1min5min93° C.3s30s2.5min
From the conventional art, various cleaning devices are known which monitor the thermal hygienization of items to be cleaned according to one or more standards. For example, WO 2006/097294 A1, which corresponds to U.S. Publication No. 20080115807, which is incorporated herein by reference, describes a method for evaluating and ensuring the thermal hygiene effect in a continuous dishwasher. Permanently fitted in the continuous dishwasher, there are one or more or sensors which record the temperature inside individual treatment zones and communicate them to a machine controller. The machine controller determines the thermal hygiene effect by means of the temperature and time respectively acting on the item to be cleaned, with the aid of heat equivalents. The washing process can be controlled so that a preset amount of heat equivalent values is applied to the item to be cleaned.
DE 10 2007 021 245 A1, which corresponds to U.S. Publication No. 20080283096, and which is incorporated herein by reference, proposes a disinfection controller for target pathogen selection. Information concerning a target germ, with which the object to be cleaned could be contaminated, is received and at least one process parameter is selected so that the target germ is killed with high probability in the cleaning process. The cleaning process is then carried out with the process parameter.
In practice, however, when using hygienization methods which are based on the recording of heat equivalents, for example according to one or more of the said standards, it has been found that the predicted hygienizations do not occur in all cases. In particular, it has been found that items to be cleaned, for example crockery, which should actually have a particular hygiene level according to the theoretical predictions of the standards, in fact have a lower hygiene level. It has furthermore been found that the measured hygiene level can sometimes depend strongly on the time which has elapsed between the hygienization and the measurement.